Exclude some stdlib gems from RBI generation #32089

Job	Run time
syntax	49s
tap syntax	6m 14s
formula audit	5m 38s
test default formula (Ubuntu 22.04)	2m 13s
cask audit	4m 10s
test default formula (Ubuntu 20.04)	2m 51s
tests (online)	4m 56s
tests (generic OS)	2m 44s
test default formula (macOS 13 x86_64)	3m 16s
update-test (Ubuntu)	17s
tests (Ubuntu 24.04)	3m 1s
test default formula (macOS 15 arm64)	1m 21s
update-test (macOS)	22s
tests (Ubuntu 22.04)	3m 0s
vendored gems	36s
tests (Ubuntu 20.04)	3m 2s
tests (macOS 13 x86_64)	10m 55s
tests (macOS 15 arm64)	4m 34s
	59m 59s

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